Process of treating a xerographic glass binder plate and product



United States Patent 3,537,848 PROCESS OF TREATING A XEROGRAPHIC GLASS BINDER PLATE AND PRODUCT Richard L. Lane, Penfield, N.Y., assignor to Xerox Corporation, Rochester, N.Y., a corporation of New York No Drawing. Continuation-impart of application Ser. No.

420,170, Dec. 21, 1964, now Patent No. 3,397,982. This application Oct. 20, 1967, Ser. No. 676,710

Int. Cl. G03g 5/04; C03c 21/00 U.S. CI. 96-15 9 Claims ABSTRACT OF THE DISCLOSURE A method of improving the humidity stability of a xerographic glass binder plate having a photoconductive layer comprising an inorganic glass binder material having photoconductive particles dispersed throughout sa1d binder, said method comprising exposing at least one surface of the photoconductive layer of said plate to heated vapors of a metal chloride, whereby a surface reaction occurs between said heated metal chloride gas and the glass photoconductive surface causing a chemical reaction characterized by a slight lightening in the color of the glass surface.

BACKGROUND OF THE INVENTION This application is a continuation-in-part of applicant's copending application Ser. No. 420,170, filed Dec. 21, 1964, now U.S. Pat. 3,397,982.

This invention relates to electrophotography and, more particularly, to a novel structure for an electrophotographic plate.

It is known to produce electrostatic images on the surface of a photoconductive insulating layer by uniformly charging the insulating layer and then dissipating this charge on that portion of the layer which is exposed to light. The latent image formed thereon will correspond to the configuration of the light image passing through the master to be reproduced. This image is rendered visible by depositing on the insulating layer a finely divided developing material comprising a colorant called a toner and a toner carrier. The developing material will be attracted to that portion of the layer retaining a charge thereby distributing itself over the layer in a manner corresponding to the electrostatic image. The powder image may then be transferred to paper or other recording surface by placing the surface of the paper in contact with the powdered layer and applying an electrostatic charge to the paper. The paper, upon being separated from the insulating layer, will bear the powdered image which may subsequently be made permanent by heating or other suitable fixing means. This general process is disclosed in detail in U.S. Pat. 2,297,691 to Carlson, and U.S. Pats. 2,357,809 and 3,079,342.

As discussed in Carlson, photoconductive insulating coatings comprise anthracene, sulfur or various mixtures of these materials such as sulfur with selenium, etc., to thereby form uniform amorphous coatings on the base material. These materials have a sensitivity largely limited to the shorter wavelengths and have a further limitation of being only slightly light-sensitive. Consequently, there has been an urgent need for improved photoconductive insulating materials.

The discovery of the photoconductiveinsulating properties of highly purified vitreous selenium has resulted in this material becoming the standard in commerical xerography. The photographic speed of this material is many times that of the prior art photoconductive insulating materials. However, vitreous selenium suffers from two serious defects: (1) its spectral response is very ice many times inthe xerographic process, so that the costper copy of such a plate may be a reasonably small figure. Under conditions of optimum use, a vitreous selenium plate can be used to prepare 100,000 or even more copies before it deteriorates to the point of unsatisfactory image formation. Under other conditions far fewer copies can be made.

The deterioration observed in selenium plates follows from the mechanical abrasion attendant to the developing process and the cleaning step wherein a rapidly rotating fur brush contacts the selenium surface to remove from the surface any developer particles adhering thereto after the transfer step. In addition to mechanical abrasion, the heat to which the plate is subjected, both by virtue of the friction involved in the various processing steps and, more important, by the propinquity of heat fusing devices generally located (by engineering necessity) in close proximity to the xerographic drum in commercial machines.

In addition, binder plates using resinous binders have been used in electrophotography. These resin-binder plates, while desirable as single use plates, have not exhibited the physical hardness for use under long processing cycles. A binder type plate having very desirable reusable properties comprises an inorganic pigment dispersed in a glass binder as disclosed in U.S. Pat. 3,l5l,- 982. In this patent, the use of a xerographic plate containing a glass binder material of various types of frits is disclosed in detail. In addition, a large number of suitable inorganic pigments were disclosed as being useful together with the above noted glass binder frits. The use of this xerographic plate (as described in U.S. Pat. 3,151,982) has a number of significant advantages over the previously used selenium and other binder type plates. A more desirable spectral response and/or speed has often been obtained by the use of such glass plates. In addition, a much more convenient commercially adaptable process has been provided than heretofore known in the manufacture of other xerographic plates.

There are, however, some inherent disadvantages to the use of glass binder plates; one being that the glass binder has a tendency to readily absorb and/or adsorb atmospheric moisture which adversely effects its reusability, and other Xerographic moisture which adversely effects its humidity or moisture, the glass surface exhibits lateral conductivity and this tends to occur at even moderately high relative humidities. In cases of severe abrasion due to cascade development, there is also evidence of high bulk conductivity characterized in a failure of the glass binder plate to retain sufficient charge for development. This causes a dissipation on the photoconductive surface of the latent electrostatic image formed thereon. This undesirable humidity sensitivity has been especially noticeable in glass frits which have a relatively high alkali content. In addition, non-alkali-containing glasses have been shown to be humidity sensitive, particularly if they have been subjected to the abrasive action of conventional cascading xerographic developers or the action of a polishing abrasive. The xerographic properties, especially the reusability of these glass binder plates has been seriously hampered by the tendency of these plates to absorb atmospheric moisture and humidity. Since one of the desirable features of commercial acceptability of glass binder plates resides in their intended reusability, the commer- 3 cial acceptance of such plates heretofore has been rather limited.

One approach to solving the above mentioned problems involves overcoating the glass binder structure with a thin oxide overcoating in order to inhibit the high humidity effects. This concept is set forth in applicants parent application Ser. No. 420,170, filed Dec. 21, 1964.

Another approach involves using organic overcoatings such as epoxides, waxes, oils, etc. Such coatings, however, tend to result in a high residual voltage or physically deteriorate due to the abrasive wear caused in developing images formed on the glass binder plate surfaces.

When either of the above two suggested techniques are used (i.e., overcoating with an oxide or organic material) the quality of the xerographic images deteriorates rapidly upon prolonged abrasive wear inherent in the developing cycle of the xerographic plate or drum.

SUMMARY OF THE INVENTION It is, therefore, an object of this invention to provide a novel glass containing xerographic plate devoid of the above noted disadvantages.

It is still another object of this invention to provide a novel system using a xerographic plate.

It is yet another object of this invention to provide a method for increasing and improving the humidity limit of an electrophotographic plate.

It is yet another object of this invention to provide a novel method for improving the reusability of a glass binder-inorganic pigment xerographic plate.

The foregoing objects and others are accomplished in accordance with this invention by providing an electrophotographic plate comprising a photoconductive layer having an inorganic glass material which acts as a binder for photoconductive particles dispersed throughout the glass binder. Plates such as those defined in U.S. Pat. 3,151,982 are representative of those included within the scope of the present invention. Such a glass binder structure is improved in its humidity limit by treating the surface with metal chloride vapors to cause either a replacement or chemical combination of the glass surface ions with the metal ions of the chloride vapor gas. Plates having a photoconductive glass layer are also included within the scope of this invention. Any suitable metal chloride is included within the scope of this invention. Typical metal chlorides are aluminum trichloride, zirconium tetrachloride, vanadium tetrachloride, silicon tetrachloride, germanium tetrachloride, titanium tetrachloride, and mixtures thereof. The above list of metal chlorides is illustrative of typical metal chlorides and should not be taken as limiting.

Aluminum trichloride and zirconium tetrachloride have been found to be preferred metal chlorides for the method of this invention for several reasons. First, the vaporization temperatures of both these compounds are particularly desirable in that they are above room temperature and yet below that of the annealing temperatures of glasses included within the scope of this invention. In addition, both aluminum trichloride and zirconium tetrachloride are solids at room temperature, and hence are easy to handle in that special treating apparatus is not required.

In order to avoid the formation of an undesirable surface coating, the moisture content of the vapor treating environment should be kept at a level which substantially prevents the hydrolysis of the metal chloride resulting in the formation of a metal oxide on the surface of the photoconductive glass. Depending upon the particular metal chloride, the amount of allowable moisture present may vary from a low of relative humidity up to the point at which the metal chloride will hydrolize to form an appreciable coating on the surface of the glass. Alternatively, the entire vapor treatment may simply be carried out in a vacuum chamber in order to insure absolute control over the moisture content.

The temperature range for treating the photoconductive glass layer may vary from the vaporization temperature of the metal chloride up to about the annealing temperature of the photoconductive glass layer. The time of treatment is usually for at least about 1 minute, although with higher temperatures the time may be reduced to less than 1 minute.

In the above defined vapor treatment, it is preferred that the plate he preheated to a temperature above that of the chloride chamber or treating environment, to prevent condensation of chloride on the plate surface, and in addition, to reduce the time necesasry for treatment.

In one embodiment of this invention, vapors of aluminum trichloride (AlCl are used to treat a preheated plate which is plunged into a chamber saturated with vapors of aluminum chloride. The instant contact of the vapor with the plate is carried out in a substantial absence of moisture content in the air. For purposes of illustration, the aluminum chloride vapor treatment of a small fiat xerographic plate is carried out as follows: A shallow tray covered with a close fitting fiat cover is allowed to fill with aluminum chloride vapors by the evaporation of solid aluminum chloride at an elevated temperature. A glass binder plate containing photosensitive particles of cadmium sulfoselenide (preheated to a temperature somewhat above the temperature of the AlCl tray to prevent immediate condensation of A101 on the plate) is positioned quickly over the tray in place of the close fitting cover. The cover of the tray is removed and the plate placed into position in such a manner that a minimum amount of moisture containing air is introduced. The exposure of air would immediately hydrolize the aluminum chloride vapors producing aluminum hydroxide which results in a tenacious aluminum oxide coating on the glass surface. The formation of this oxide coating is to be avoided inasmuch as oxide coatings give inferior xerographic properties after abrasive wear, as opposed to the product of the instant treatment. After this treatment the plate is removed, cooled, Washed with water, and rubbed dry with a clean cloth.

If the above treatment is to be carried out under vacuum conditions, the glass binder plate to be treated is suspended in a vacuum chamber several inches above a source of a suitable metal chloride contained in an inert crucible. Any suitable vacuum such as from about 10- to 10 torr is maintained in the chamber. The plate is preheated to a temperature up to the annealing point of the glass by any suitable heating means such as a backing hot plate or heating coil. When the glass plate has reached the preheat temperature, the source of metal chloride is vaporized by heating it to its vaporization temperature. The vapors of the metal chloride are reacted with the heated glass plate for at least about one minute. After the vapor treatment, the plate is cooled to room temperature the vacuum broken, and the treated plate removed from the chamber.

Properly carried out, the chlorine treatment of this invention results in a hydrophobic glass surface, slightly lighter in color than the original surface, with no evidence of a surface deposit or overcoating.

Optimum conditions for aluminum chloride employing the above technique for the glass binder plate were determined to be a preheated plate temperature of about 325 C., (approximate annealing temperature) a vapor temperature of about 225 C., and a reaction period of about 1 minute. Under these conditions, the humidity cutoff point or limit is raised to above relative humidity, and the initial potential is increased under identical charging conditions. With proper care, the results of this process are quite reproducible on all glass xerographic type plates, whether they be of the binder-type disclosed in the above mentioned U.S. Pat. 3,151,982 or a photoconductive glass.

The humidity limit or humidity cutoff point of glass binder plates which have not been treated by the method of the instant invention, usually is well under 50% relative humidity with most of the untreated plates having a humidity limit in the range of 20 to 40%. By the term humidity limit or cutoff point is meant for the purposes of this invention, the amount of humidity that a plate can tolerate and yet be imagable. Through the use of the novel treatment of this invention, humidity limits are increased to at least 50% and in most cases to a preferred level of at least 65% for both alkali glass containing plates and non-alkali glass containing plates. Values up to 85% relative humidity and higher are particularly preferred in that these plates have the greatest stability.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The following examples specifically define the present invention with respect to a method of treating a xerographic glass binder plate. The parts and percentages in the disclosure, examples, and claims are by weight unless otherwise indicated. The examples are intended to illustrate the various preferred embodiments of making and treating a glass binder plate.

EXAMPLE I A series of eight experimental plates are made from an alkali glass frit having the following composition:

Parts SiO, 46 Na O 15 B 7 PhD 17 CdO TiO, 6 CaO I 3 K 0 1 EXAMPLE II Four of the plates (designated Plates 1-4) are then treated by the following method:

A shallow alumina tiay covered with a close fitting flat cover is allowed to fill with aluminum chloride vapors by the vaporization of solid aluminum chloride at a temperature of about 225 C. A plate made by the method of Example I is preheated to a temperature of about 325 C. \and quickly positioned over the tray in place of the cover. Care is taken to assure that when the cover is replaced with the plate that a minimum amount of moisture-containing air is introduced. This precaution is taken to keep the air from hydrolyzing the aluminum chloride vapors, producing aluminum hydroxide which results in a tenacious aluminum oxide coating being formed on the glass surface. This treatment is carried out for about 1 minute. The plate is then cooled to room temperature, washed with deionized water to remove any possible residual chlorides, and rubbed dry with a clean cloth. This treatment results in the formation of a hydrophobic glass surface, slightly lighter in color than the original surface. There is no evidence of a surface deposit.

Each of the remaining 3 plates is treated by the above method. The plates are then xerographically imaged. All treated plates exhibit excellent xerographic reproduction characteristics with electronic measurements indicating that the humidity cutofl point was greater than 85% relafive humidity. The print quality is observed to be constant in a measured range of 30 to 75% relative humidity. The xerographic speed of the plates is approximately six times that of selenium to tungsten light.

EXAMPLE III Plates 5-8, which have not been treated with chloride vapors, are also xerographically tested for print quality in a measured humidity range of 30 to 70%. Although these plates gave faint reproductions of an original image in a humidity-range of about 35% they failed to produce images at a humidity in excess of about 40%.

EXAMPLE IV To test the relationship of abrasion resistance to print quality of the chloride treated glass plates (Plates 1-4) as compared to untreated plates (Plates 5-8), the following test conditions are used:

The plates are tested to withstand the abrasive action of cascading a sand carrier material by taping the plates to the bottom of a metal pan containing a known quantity of uncoated silica sand. The pan is then placed on a Central Scientific Co. vibrating sieve shaker whrch causes the sand to impact upon the surface of the glass. The sieve shaker is placed on a setting of 6 which results in about 3,000 vibrations per minute. For an untreated plate, 1 to 5 minutes of this abrasion test is sufficient to lower the humidity cutoff point to below 40% relative humidity. However, an aluminum chloride treated plate is unaffected by minutes of such a treatment.

Test results similar to those described above were also determined for a typical non-alkali glass frit having the following glass composition:

This frit was also mixed with 25% by weight of the cadmium sulfoselenide defined in Example I.

Although the above tests are not an actual equivalent for the cascade abrasive effect in xerographic develop ment, it is regarded as being indicative of the abrasive effect during development in xerography after thousands of cycles. In any case, the results of these tests are felt to be significant inasmuch as they indicate that the stabilized surfaces (i.e., those treated with the metal chloride) would not be adversely afiected by cascade development in machine operation.

Although specific components and proportions have been stated in the above description of the preferred embodiments of this invention, other suitable materials and procedures such as those listed above may be used with similar results. In addition, other materials may be added to the plates which synergize, enhance, or otherwise modify their properties.

Other modifications and ramifications of the present invention would appear to those skilled in the art upon reading the disclosure. These are intended to be included within the scope of this invention.

What is claimed is:

1. A method of improving the humidity stability of a xerographic glass binder plate having a photoconductive layer comprising an inorganic glass binder material having photoconductive particles dispersed throughout said binder, said method comprising exposing at least one surface of the photoconductive layer of said plate to heated vapors of a metal chloride selected from the group consisting of zirconium tetrachloride, vanadium tetrachloride, aluminum trichloride, silicon tetrachloride, germanium tetrachloride, titanium tetrachloride, and mixtures thereof, wherein the moisture content of the vapor treating environment is kept at a level which substantially prevents the hydrolysis of the metal chloride, whereby a surface reaction occurs between said heated metal chloride gas and the glass photoconductive surface characterized by a slight lightening in the color of the glass surface.

2. The method of claim 1 wherein the metal chloride comprises aluminum trichloride.

3. The method of claim 1 wherein the metal chloride comprises zirconium tetrachloride.

4. The method of claim 1 wherein the xerographic plate is preheated prior to treating with the heated metal chloride gas.

5. The method of claim 4 wherein the plate is preheated to a temperature of about 325 C., and then treated with the metal chloride gas at about 225 C. for about one minute.

6. A method of improving the humidity stability of a photosensitive member having a photoconductive glass layer, said method comprising preheating the photoconductive layer to a temperature up to the annealing temperature of the glass, exposing at least one surface of said glass layer to heated vapors of a metal chloride selected 20 from the group consisting of zirconium tetrachloride, vanadium tetrachloride, aluminum trichloride, silicon tetrachloride, germanium tetrachloride, titanium tetrachloride, and mixtures thereof, wherein the moisture content of the vapor treating environment is kept at a level which substantially prevents the hydrolysis of the metal 8 chloride, whereby a surface reaction occurs between said vapors and said glass surface free from any evidence of a surface deposit or overcoating.

7. The method of claim 6 in which the vapor treatment is carried out in a substantial vacuum.

8. The method of claim 6 in which the photoconductive layer comprises an inorganic glass binder material having photoconductive particles dispersed in said binder.

9. The product formed by the process of claim 6.

References Cited UNITED STATES PATENTS 2,779,690 1/1957 Gaiser 117124 X 3,288,603 11/1966 Corrsin 96--l.5 3,353,514 11/1967 Lyle 65-30 X 3,369,880 2/1968 Mochel 65-30 3,397,982 8/1968 Lane 96-15 3,403,015 9/1968 Grubb et a1 117124 3,459,522 8/ 1969 Elmer et al. 65---30 GEORGE F. LESMES, Primary Examiner C. E. VAN HORN, Assistant Examiner US. Cl. X.R. 

